Coded passive transponder cards are proposed for the detection and localization of underground cooperative objects. The detection system active transmitter antenna polarization, gain and beam grazing angles are investigated to achieve maximum energy transmission to ground and to the passive transponder cards connected to the objects to be detected and localized. The detection probability can be significantly enhanced by applying space and polarization diversity of two transponder cards with two orthogonal polarized antennae on each cooperative object. Methods are suggested for improving the performances and the reliability of the objects detection and localization systems.